<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <div id="test">
    <p v-bind="obj">aaaaaaa</p>
  </div>

  <script src="../js/vue.js"></script>
  <script>
    const vm = new Vue({
      el: '#test',
      data: {
        obj: {
          a: 1,
          b: 2
        }
      }
    })

    setTimeout(() => {
      vm.obj = {
        ...vm.obj,
        c: 3
      }
    }, 2000);
  </script>
</body>
</html>